The present invention relates to a hydraulic control device for a starting device.
An automatic transmission mounted in a vehicle such as an automobile typically includes a torque converter as a starting device. The torque converter uses hydraulic transmission between an engine and an automatic speed change mechanism, for example, when starting, to absorb rotational differences between a driving wheel in a stationary state and an engine in a rotating state, and to transmit a driving force. Recently, such a torque converter includes a lock-up clutch that locks up an output shaft of the engine and an input shaft of the automatic speed change mechanism so as to reduce a transmission loss that accompanies a hydraulic transmission.
In such a lock-up clutch, which is conventionally proposed as a multi-plate type, the inside of a torque converter case is structured so as to be separated into a hydraulic oil chamber for the lock-up clutch and a transmission oil chamber in which a hydraulic transmission portion is arranged (see Japanese Patent Application Publication No. JP-A-2001-173764).
The lock-up clutch is structured so that, when hydraulic pressure is supplied to the hydraulic oil chamber and the hydraulic pressure in the hydraulic oil chamber rises above the hydraulic pressure in the transmission oil chamber, a piston is pressed to drive and a friction plate is engaged; thus setting the lock-up clutch to lock-up on. In addition, when the hydraulic pressure is supplied to the transmission oil chamber and the hydraulic pressure in the transmission oil chamber rises above the hydraulic pressure in the hydraulic oil chamber, the piston is pressed in a reverse direction; thus setting the lock-up clutch to lock-up off.